US5228974A - Electrochemical measuring cell for determining ammonia or hydrazine in a measuring sample - Google Patents
Electrochemical measuring cell for determining ammonia or hydrazine in a measuring sample Download PDFInfo
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- US5228974A US5228974A US07/804,722 US80472291A US5228974A US 5228974 A US5228974 A US 5228974A US 80472291 A US80472291 A US 80472291A US 5228974 A US5228974 A US 5228974A
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- QGZKDVFQNNGYKY-UHFFFAOYSA-N Ammonia Chemical compound N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 title claims abstract description 62
- OAKJQQAXSVQMHS-UHFFFAOYSA-N Hydrazine Chemical compound NN OAKJQQAXSVQMHS-UHFFFAOYSA-N 0.000 title claims abstract description 45
- 229910021529 ammonia Inorganic materials 0.000 title claims abstract description 29
- 239000003792 electrolyte Substances 0.000 claims abstract description 59
- 150000003839 salts Chemical class 0.000 claims abstract description 18
- 239000007864 aqueous solution Substances 0.000 claims abstract description 11
- 229910052783 alkali metal Inorganic materials 0.000 claims abstract description 8
- 150000001340 alkali metals Chemical class 0.000 claims abstract description 8
- 239000000203 mixture Substances 0.000 claims abstract description 7
- 238000000576 coating method Methods 0.000 claims description 35
- 239000011248 coating agent Substances 0.000 claims description 34
- 229910000428 cobalt oxide Inorganic materials 0.000 claims description 22
- IVMYJDGYRUAWML-UHFFFAOYSA-N cobalt(ii) oxide Chemical compound [Co]=O IVMYJDGYRUAWML-UHFFFAOYSA-N 0.000 claims description 22
- 239000012528 membrane Substances 0.000 claims description 12
- 150000001868 cobalt Chemical class 0.000 claims description 11
- UFMZWBIQTDUYBN-UHFFFAOYSA-N cobalt dinitrate Chemical compound [Co+2].[O-][N+]([O-])=O.[O-][N+]([O-])=O UFMZWBIQTDUYBN-UHFFFAOYSA-N 0.000 claims description 8
- 229910001981 cobalt nitrate Inorganic materials 0.000 claims description 8
- 239000012530 fluid Substances 0.000 claims description 8
- 239000000243 solution Substances 0.000 claims description 6
- 229910045601 alloy Inorganic materials 0.000 claims description 5
- 239000000956 alloy Substances 0.000 claims description 5
- 229910000531 Co alloy Inorganic materials 0.000 claims description 4
- 230000008014 freezing Effects 0.000 claims description 4
- 238000007710 freezing Methods 0.000 claims description 4
- 230000009467 reduction Effects 0.000 claims description 3
- 125000002091 cationic group Chemical group 0.000 claims 6
- 229910052784 alkaline earth metal Inorganic materials 0.000 claims 5
- 150000001342 alkaline earth metals Chemical class 0.000 claims 5
- 125000000129 anionic group Chemical group 0.000 claims 5
- 229910000510 noble metal Inorganic materials 0.000 claims 3
- 230000001590 oxidative effect Effects 0.000 claims 3
- OYPRJOBELJOOCE-UHFFFAOYSA-N Calcium Chemical compound [Ca] OYPRJOBELJOOCE-UHFFFAOYSA-N 0.000 claims 2
- VEXZGXHMUGYJMC-UHFFFAOYSA-M Chloride anion Chemical compound [Cl-] VEXZGXHMUGYJMC-UHFFFAOYSA-M 0.000 claims 2
- FYYHWMGAXLPEAU-UHFFFAOYSA-N Magnesium Chemical compound [Mg] FYYHWMGAXLPEAU-UHFFFAOYSA-N 0.000 claims 2
- 229910002651 NO3 Inorganic materials 0.000 claims 2
- NHNBFGGVMKEFGY-UHFFFAOYSA-N Nitrate Chemical compound [O-][N+]([O-])=O NHNBFGGVMKEFGY-UHFFFAOYSA-N 0.000 claims 2
- 229910052791 calcium Inorganic materials 0.000 claims 2
- 239000011575 calcium Substances 0.000 claims 2
- 229910052749 magnesium Inorganic materials 0.000 claims 2
- 239000011777 magnesium Substances 0.000 claims 2
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 claims 1
- 229910052744 lithium Inorganic materials 0.000 claims 1
- ZCCIPPOKBCJFDN-UHFFFAOYSA-N calcium nitrate Chemical compound [Ca+2].[O-][N+]([O-])=O.[O-][N+]([O-])=O ZCCIPPOKBCJFDN-UHFFFAOYSA-N 0.000 abstract description 8
- IIPYXGDZVMZOAP-UHFFFAOYSA-N lithium nitrate Chemical compound [Li+].[O-][N+]([O-])=O IIPYXGDZVMZOAP-UHFFFAOYSA-N 0.000 abstract description 8
- 230000004044 response Effects 0.000 abstract description 5
- 238000006243 chemical reaction Methods 0.000 description 8
- 238000005259 measurement Methods 0.000 description 8
- 230000035945 sensitivity Effects 0.000 description 8
- 230000003647 oxidation Effects 0.000 description 7
- 238000007254 oxidation reaction Methods 0.000 description 7
- 239000012876 carrier material Substances 0.000 description 5
- 239000007789 gas Substances 0.000 description 5
- 230000008901 benefit Effects 0.000 description 4
- 239000011521 glass Substances 0.000 description 3
- PCHJSUWPFVWCPO-UHFFFAOYSA-N gold Chemical compound [Au] PCHJSUWPFVWCPO-UHFFFAOYSA-N 0.000 description 3
- 229910052737 gold Inorganic materials 0.000 description 3
- 239000010931 gold Substances 0.000 description 3
- 229910052739 hydrogen Inorganic materials 0.000 description 3
- 239000001257 hydrogen Substances 0.000 description 3
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 3
- UGFAIRIUMAVXCW-UHFFFAOYSA-N Carbon monoxide Chemical compound [O+]#[C-] UGFAIRIUMAVXCW-UHFFFAOYSA-N 0.000 description 2
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 2
- 229910002091 carbon monoxide Inorganic materials 0.000 description 2
- 229910017052 cobalt Inorganic materials 0.000 description 2
- 239000010941 cobalt Substances 0.000 description 2
- GUTLYIVDDKVIGB-UHFFFAOYSA-N cobalt atom Chemical compound [Co] GUTLYIVDDKVIGB-UHFFFAOYSA-N 0.000 description 2
- 239000007788 liquid Substances 0.000 description 2
- YIXJRHPUWRPCBB-UHFFFAOYSA-N magnesium nitrate Chemical compound [Mg+2].[O-][N+]([O-])=O.[O-][N+]([O-])=O YIXJRHPUWRPCBB-UHFFFAOYSA-N 0.000 description 2
- 229910000069 nitrogen hydride Inorganic materials 0.000 description 2
- 238000001139 pH measurement Methods 0.000 description 2
- 230000035699 permeability Effects 0.000 description 2
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 description 2
- FGIUAXJPYTZDNR-UHFFFAOYSA-N potassium nitrate Chemical compound [K+].[O-][N+]([O-])=O FGIUAXJPYTZDNR-UHFFFAOYSA-N 0.000 description 2
- 239000000126 substance Substances 0.000 description 2
- 239000002585 base Substances 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 230000000903 blocking effect Effects 0.000 description 1
- 230000003197 catalytic effect Effects 0.000 description 1
- 238000006555 catalytic reaction Methods 0.000 description 1
- 150000001768 cations Chemical class 0.000 description 1
- 239000007795 chemical reaction product Substances 0.000 description 1
- 229940011182 cobalt acetate Drugs 0.000 description 1
- QAHREYKOYSIQPH-UHFFFAOYSA-L cobalt(II) acetate Chemical compound [Co+2].CC([O-])=O.CC([O-])=O QAHREYKOYSIQPH-UHFFFAOYSA-L 0.000 description 1
- 238000001514 detection method Methods 0.000 description 1
- 238000006073 displacement reaction Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 230000005518 electrochemistry Effects 0.000 description 1
- 239000007772 electrode material Substances 0.000 description 1
- 239000008151 electrolyte solution Substances 0.000 description 1
- 238000011156 evaluation Methods 0.000 description 1
- -1 hydrogen ions Chemical class 0.000 description 1
- 150000002500 ions Chemical class 0.000 description 1
- 229910052741 iridium Inorganic materials 0.000 description 1
- GKOZUEZYRPOHIO-UHFFFAOYSA-N iridium atom Chemical compound [Ir] GKOZUEZYRPOHIO-UHFFFAOYSA-N 0.000 description 1
- 230000007774 longterm Effects 0.000 description 1
- 238000000034 method Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 150000004767 nitrides Chemical class 0.000 description 1
- 238000002161 passivation Methods 0.000 description 1
- 229910052697 platinum Inorganic materials 0.000 description 1
- 239000002574 poison Substances 0.000 description 1
- 231100000614 poison Toxicity 0.000 description 1
- 235000010333 potassium nitrate Nutrition 0.000 description 1
- 239000004323 potassium nitrate Substances 0.000 description 1
- 239000010970 precious metal Substances 0.000 description 1
- 238000012545 processing Methods 0.000 description 1
- 239000000047 product Substances 0.000 description 1
- 230000036647 reaction Effects 0.000 description 1
Images
Classifications
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
- G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
- G01N27/403—Cells and electrode assemblies
- G01N27/404—Cells with anode, cathode and cell electrolyte on the same side of a permeable membrane which separates them from the sample fluid, e.g. Clark-type oxygen sensors
- G01N27/4045—Cells with anode, cathode and cell electrolyte on the same side of a permeable membrane which separates them from the sample fluid, e.g. Clark-type oxygen sensors for gases other than oxygen
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
- G01N33/0004—Gaseous mixtures, e.g. polluted air
- G01N33/0009—General constructional details of gas analysers, e.g. portable test equipment
- G01N33/0027—General constructional details of gas analysers, e.g. portable test equipment concerning the detector
- G01N33/0036—General constructional details of gas analysers, e.g. portable test equipment concerning the detector specially adapted to detect a particular component
- G01N33/0054—Ammonia
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
- Y02A50/00—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE in human health protection, e.g. against extreme weather
- Y02A50/20—Air quality improvement or preservation, e.g. vehicle emission control or emission reduction by using catalytic converters
Definitions
- the invention relates to an electrochemical measuring cell for determining ammonia or hydrazine in a fluid (gaseous or liquid) measuring sample.
- the measuring cell has at least one measuring electrode and at least one counter electrode which are arranged in an electrolyte chamber filled with a soluble electrolyte.
- the electrolyte chamber is closed off with respect to the measuring sample by a permeable membrane.
- An electrochemical measuring cell of this kind is disclosed in U.S. Pat. No. 3,649,505 and includes a pH-electrode as a measuring electrode which is used to measure hydrogen ions.
- This potentiometric measurement of an ammonia concentration requires a long time duration for a completed measuring reaction. The long time duration is needed for the adjustment of an equilibrium. In this time duration, the NH 3 to be detected and the water content of the electrolyte conjointly form NH 4 OH which, in turn, dissociates into NH 4 + ions and OH - ions.
- the slow step determining the speed for this reaction is the adjustment of the equilibrium with the gas space or the adjustment of the equilibrium at the glass membrane.
- the glass electrode required for the pH-measurement changes in the characteristic of the glass membrane in the course of its use so that drift phenomena occur.
- a stable reference potential is necessary for carrying out the pH-measurement and a displacement of this reference potential in the course of use likewise leads to drift phenomena.
- the known measuring cell responds to all gases influencing the pH-value of the electrolyte so that its selectivity for measurements in corresponding gas mixtures is not adequate.
- the electrochemical measuring cell of the invention is for determining ammonia or hydrazine in a fluid measuring sample.
- the measuring cell includes: a housing having an opening directed toward the sample to be measured and defining an electrolyte chamber; a soluble electrolyte contained in the chamber; a permeable membrane mounted on the housing for closing off the chamber; a measuring electrode and a counter electrode disposed in the chamber so as to be in spaced relationship to each other; and, the measuring electrode having a coating containing cobalt oxide and the coating being formed on the measuring electrode so as to be in direct contact with the electrolyte.
- the advantage of the invention is essentially that the oxidation of the ammonia at the measuring electrode is catalyzed by the cobalt oxide coating so that no disturbing secondary products develop at the measuring electrode which could hinder an oxidation which follows. Furthermore, no blocking of the electrode occurs because of an electrochemically inert passive layer.
- the measuring cell according to the invention affords the advantage that it offers a very good long-term stability and negligible drift. Also, very high concentrations of ammonia can be measured because of the catalytically effective oxide layer. These high concentrations are rendered harmless with respect to catalytic poisons or disadvantageous influences of the electrolyte for the operational capability of the measuring cell. Because of the coating of cobalt oxide, the oxidation of ammonia at the measuring electrode surface occurs so rapidly that the ammonia concentration at this electrode surface is practically zero. This results in a high concentration gradient between the measuring sample and the surface of the measuring electrode. In this way, the measuring cell reaction is returned to a transport-controlled reaction without restrictive reaction steps. This leads to a rapid response time and to a high sensitivity of the measuring cell. Gold, platinum or iridium can be selected as a carrier material for the electrode. The measuring cell of the invention is equally well suited for detecting hydrazine.
- a carrier material of gold defining the electrode can, for example, be dipped into a cobalt nitrate solution or a cobalt acetate solution and cobalt oxide is then electrically deposited thereon. Potassium nitrate can be added to the cobalt solution as a conductive electrolyte.
- Another method for forming the cobalt oxide coating is to form the carrier material for the electrode from a cobalt-containing alloy which is then oxidized.
- Carrier materials for electrochemically measuring ammonia can be used by applying the coating containing cobalt oxide. Without this coating, a surface passivation in the form of a nitride formation occurs whereby the measuring sensitivity is reduced to the point that the measuring cell is unusable.
- a reference electrode is introduced into the measuring cell having a potential which functions as a reference point for the measurement. It is advantageous to likewise provide such a reference electrode with a coating containing cobalt oxide.
- a measuring cell of this kind affords the advantage that it can be stored with short-circuited electrodes whereby it is immediately operationally ready because of the short warm-up time. Furthermore, the dependency of the residual current on temperature is minimized since the potential of the measuring electrode and of the reference electrode are influenced in the same manner by the temperature.
- U.S. Pat. No. 5,076,904 discloses a measuring cell wherein the NH 3 molecules diffuse from the gas phase through the porous membrane and a thin electrolyte film to the electrode where they are anodically oxidized.
- the permeability of the gas to be measured in the electrolyte film is essential for a high sensitivity of the sensor.
- the minimum operating temperature of the sensor is limited by the freezing point of the electrolyte while the service life of the sensor is determined primarily by the water vapor pressure of the electrolyte.
- the above object is achieved by providing as an electrolyte, an aqueous solution of a hygroscopic salt of an alkali metal or an earth alkali metal or a mixture of both salts.
- the hygroscopic salts effect a reduction of the freezing point so that the sensors can be utilized down to a temperature of -50° C. in refrigerating plants or in open air.
- the water vapor pressure of the electrolyte solution is reduced so that the liquid loss is slowed and a large electrolyte reservoir is unnecessary.
- a hygroscopic salt such as lithium nitrate, magnesium nitrate or calcium nitrate or a mixture of these salts is selected, then ammonia and hydrazine form complexes or complex-type bonds with the cations. In this way, the solubility and the permeability and therefore the sensitivity is increased.
- the measuring electrode with a coating containing cobalt oxide with the coating being so applied on the measuring electrode that the electrode is in direct contact with the electrolyte.
- An improved protection of the measuring electrode surface against disturbing reactions of reaction products is obtained with the cobalt oxide coating.
- the measuring electrode and reference electrode can preferably be made of a precious metal such as gold with the coating being deposited electrolytically on the carrier material of the electrode.
- the measuring electrode and the reference electrode from a carrier which comprises a cobalt alloy and with the coating being formed from an oxide layer which is obtained by oxidation of the alloy.
- the cobalt salt acts as a catalyzer in that it regenerates the cobalt oxide coating if the coating should become damaged during operation of the measuring cell. Furthermore, the cobalt salt supports the catalytic reaction of the ammonia oxidation or hydrazine oxidation at the measuring electrode in the electrolyte. In this way, the sensitivity and the response speed of the chemical measuring cell are increased.
- An advantageous cobalt salt for this purpose is cobalt nitrate.
- the cobalt salt and especially cobalt nitrate By using the cobalt salt and especially cobalt nitrate, the generation of a new cobalt oxide layer is favored insofar as it is attacked by a chemical disturbance reaction.
- An especially suitable mixture for the electrolyte is a 3.5 molar solution of calcium nitrate or lithium nitrate and a 0.1 millimolar cobalt nitrate admixture as a catalyzer. The admixture of cobalt nitrate can be increased up to 1 millimol without the detection function of the measuring cell being affected.
- the electrochemical measuring cell of the invention has no cross sensitivity with respect to carbon monoxide and hydrogen.
- a reference electrode is introduced into the measuring cell to generate a reference potential for the determination of ammonia or hydrazine.
- the potential of the reference electrode defines a reference point for the measurement. It is advantageous to likewise provide such a reference electrode with a coating containing cobalt oxide.
- a measuring cell of this kind affords the advantage that the cell can be stored with its electrodes short circuited whereby the cell is immediately operationally ready because of the short run-in time. Furthermore, the dependence of the base current on the temperature is minimized since the potential of the measuring electrode and the reference electrode is influenced in the same manner by the temperature.
- the electrochemical measuring cell includes an electrolyte 3 of an aqueous solution of calcium nitrate and lithium nitrate.
- the electrolyte is contained in a housing 4 in which a measuring electrode 1, a counter electrode 2 and a reference electrode 9 are introduced.
- the electrodes (1, 9) have respective coatings (11, 12) containing cobalt oxide.
- the electrolyte 3 is closed off in a direction facing toward the ambient containing the measuring sample by a membrane 5 which is permeable to ammonia and hydrazine and which is attached to the housing 4 in a seal-tight manner.
- the measuring electrode 1, the counter electrode 2 and the reference electrode 9 have respective measurement leads (6, 7, 10) which are passed through the housing 4 and connected to an evaluation device 8 for processing the measurement signals.
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Abstract
The invention is directed to an electrochemical measuring cell for measuring ammonia or hydrazine and includes at least a measuring electrode and a counter electrode in an electrolyte. The measuring cell provides a signal increase having a shorter response time and an improved signal stability. For this purpose, the electrolyte is an aqueous solution of a hygroscopic salt of an alkali metal or earth alkali metal such as calcium nitrate or lithium nitrate or a mixture of both salts.
Description
This is a continuation-in-part of application Ser. No. 507,755, filed Apr. 12, 1990, which has issued as U.S. Pat. No. 5,076,904.
The invention relates to an electrochemical measuring cell for determining ammonia or hydrazine in a fluid (gaseous or liquid) measuring sample. The measuring cell has at least one measuring electrode and at least one counter electrode which are arranged in an electrolyte chamber filled with a soluble electrolyte. The electrolyte chamber is closed off with respect to the measuring sample by a permeable membrane.
An electrochemical measuring cell of this kind is disclosed in U.S. Pat. No. 3,649,505 and includes a pH-electrode as a measuring electrode which is used to measure hydrogen ions. This potentiometric measurement of an ammonia concentration requires a long time duration for a completed measuring reaction. The long time duration is needed for the adjustment of an equilibrium. In this time duration, the NH3 to be detected and the water content of the electrolyte conjointly form NH4 OH which, in turn, dissociates into NH4 + ions and OH- ions. The slow step determining the speed for this reaction is the adjustment of the equilibrium with the gas space or the adjustment of the equilibrium at the glass membrane.
The glass electrode required for the pH-measurement changes in the characteristic of the glass membrane in the course of its use so that drift phenomena occur. A stable reference potential is necessary for carrying out the pH-measurement and a displacement of this reference potential in the course of use likewise leads to drift phenomena. The known measuring cell responds to all gases influencing the pH-value of the electrolyte so that its selectivity for measurements in corresponding gas mixtures is not adequate.
It is an object of the invention to provide an electrochemical measuring cell of the kind described above which is improved so that a selective ammonia measurement is obtained providing the following: short response time, a linear response and a low tendency to drift. It is a further object of the invention to provide such an electrochemical measuring cell having electrodes which are so configured that the oxidation of the ammonia or hydrazine as a measurement reaction has no influence on the sensitivity of this measuring cell.
The electrochemical measuring cell of the invention is for determining ammonia or hydrazine in a fluid measuring sample. The measuring cell includes: a housing having an opening directed toward the sample to be measured and defining an electrolyte chamber; a soluble electrolyte contained in the chamber; a permeable membrane mounted on the housing for closing off the chamber; a measuring electrode and a counter electrode disposed in the chamber so as to be in spaced relationship to each other; and, the measuring electrode having a coating containing cobalt oxide and the coating being formed on the measuring electrode so as to be in direct contact with the electrolyte.
The advantage of the invention is essentially that the oxidation of the ammonia at the measuring electrode is catalyzed by the cobalt oxide coating so that no disturbing secondary products develop at the measuring electrode which could hinder an oxidation which follows. Furthermore, no blocking of the electrode occurs because of an electrochemically inert passive layer.
The measuring cell according to the invention affords the advantage that it offers a very good long-term stability and negligible drift. Also, very high concentrations of ammonia can be measured because of the catalytically effective oxide layer. These high concentrations are rendered harmless with respect to catalytic poisons or disadvantageous influences of the electrolyte for the operational capability of the measuring cell. Because of the coating of cobalt oxide, the oxidation of ammonia at the measuring electrode surface occurs so rapidly that the ammonia concentration at this electrode surface is practically zero. This results in a high concentration gradient between the measuring sample and the surface of the measuring electrode. In this way, the measuring cell reaction is returned to a transport-controlled reaction without restrictive reaction steps. This leads to a rapid response time and to a high sensitivity of the measuring cell. Gold, platinum or iridium can be selected as a carrier material for the electrode. The measuring cell of the invention is equally well suited for detecting hydrazine.
For producing a cobalt oxide coating, a carrier material of gold defining the electrode can, for example, be dipped into a cobalt nitrate solution or a cobalt acetate solution and cobalt oxide is then electrically deposited thereon. Potassium nitrate can be added to the cobalt solution as a conductive electrolyte. Another method for forming the cobalt oxide coating is to form the carrier material for the electrode from a cobalt-containing alloy which is then oxidized.
Carrier materials for electrochemically measuring ammonia can be used by applying the coating containing cobalt oxide. Without this coating, a surface passivation in the form of a nitride formation occurs whereby the measuring sensitivity is reduced to the point that the measuring cell is unusable. In this connection, reference may be made to the "Encyclopedia of Electrochemistry of the Elements", Volume 8, 1978, page 413.
With respect to the measuring cell of the invention, it is emphasized that there is no cross-sensitivity against carbon monoxide or hydrogen.
In order to generate a reference potential for determining ammonia or hydrazine, a reference electrode is introduced into the measuring cell having a potential which functions as a reference point for the measurement. It is advantageous to likewise provide such a reference electrode with a coating containing cobalt oxide. A measuring cell of this kind affords the advantage that it can be stored with short-circuited electrodes whereby it is immediately operationally ready because of the short warm-up time. Furthermore, the dependency of the residual current on temperature is minimized since the potential of the measuring electrode and of the reference electrode are influenced in the same manner by the temperature.
U.S. Pat. No. 5,076,904 discloses a measuring cell wherein the NH3 molecules diffuse from the gas phase through the porous membrane and a thin electrolyte film to the electrode where they are anodically oxidized. The permeability of the gas to be measured in the electrolyte film is essential for a high sensitivity of the sensor. The minimum operating temperature of the sensor is limited by the freezing point of the electrolyte while the service life of the sensor is determined primarily by the water vapor pressure of the electrolyte.
Accordingly, it is still another object of the invention to improve a measuring cell of the kind described in the above-mentioned European patent application to increase the sensitivity as well as to lower the operating temperature and increase the service life.
The above object is achieved by providing as an electrolyte, an aqueous solution of a hygroscopic salt of an alkali metal or an earth alkali metal or a mixture of both salts.
The hygroscopic salts effect a reduction of the freezing point so that the sensors can be utilized down to a temperature of -50° C. in refrigerating plants or in open air. The water vapor pressure of the electrolyte solution is reduced so that the liquid loss is slowed and a large electrolyte reservoir is unnecessary.
If, as an example, a hygroscopic salt such as lithium nitrate, magnesium nitrate or calcium nitrate or a mixture of these salts is selected, then ammonia and hydrazine form complexes or complex-type bonds with the cations. In this way, the solubility and the permeability and therefore the sensitivity is increased.
To further improve the electrochemical measuring cell, it is advantageous to provide the measuring electrode with a coating containing cobalt oxide with the coating being so applied on the measuring electrode that the electrode is in direct contact with the electrolyte. An improved protection of the measuring electrode surface against disturbing reactions of reaction products is obtained with the cobalt oxide coating.
If a so-called three-electrode measuring cell is utilized, then it is advantageous to provide a reference electrode in the electrolyte which likewise has a coating containing cobalt oxide.
The measuring electrode and reference electrode can preferably be made of a precious metal such as gold with the coating being deposited electrolytically on the carrier material of the electrode.
It can be just as advantageous to produce the measuring electrode and the reference electrode from a carrier which comprises a cobalt alloy and with the coating being formed from an oxide layer which is obtained by oxidation of the alloy.
For an electrode material having a cobalt oxide coating, it is advantageous to add a soluble cobalt salt to the electrolyte. The cobalt salt acts as a catalyzer in that it regenerates the cobalt oxide coating if the coating should become damaged during operation of the measuring cell. Furthermore, the cobalt salt supports the catalytic reaction of the ammonia oxidation or hydrazine oxidation at the measuring electrode in the electrolyte. In this way, the sensitivity and the response speed of the chemical measuring cell are increased.
An advantageous cobalt salt for this purpose is cobalt nitrate. By using the cobalt salt and especially cobalt nitrate, the generation of a new cobalt oxide layer is favored insofar as it is attacked by a chemical disturbance reaction. An especially suitable mixture for the electrolyte is a 3.5 molar solution of calcium nitrate or lithium nitrate and a 0.1 millimolar cobalt nitrate admixture as a catalyzer. The admixture of cobalt nitrate can be increased up to 1 millimol without the detection function of the measuring cell being affected.
It is emphasized that the electrochemical measuring cell of the invention has no cross sensitivity with respect to carbon monoxide and hydrogen.
A reference electrode is introduced into the measuring cell to generate a reference potential for the determination of ammonia or hydrazine. The potential of the reference electrode defines a reference point for the measurement. It is advantageous to likewise provide such a reference electrode with a coating containing cobalt oxide.
A measuring cell of this kind affords the advantage that the cell can be stored with its electrodes short circuited whereby the cell is immediately operationally ready because of the short run-in time. Furthermore, the dependence of the base current on the temperature is minimized since the potential of the measuring electrode and the reference electrode is influenced in the same manner by the temperature.
The invention will now be described with reference to the single figure of the drawing which is a side elevation view, in section, of a measuring cell according to the invention.
The electrochemical measuring cell includes an electrolyte 3 of an aqueous solution of calcium nitrate and lithium nitrate. The electrolyte is contained in a housing 4 in which a measuring electrode 1, a counter electrode 2 and a reference electrode 9 are introduced. The electrodes (1, 9) have respective coatings (11, 12) containing cobalt oxide. The electrolyte 3 is closed off in a direction facing toward the ambient containing the measuring sample by a membrane 5 which is permeable to ammonia and hydrazine and which is attached to the housing 4 in a seal-tight manner. The measuring electrode 1, the counter electrode 2 and the reference electrode 9 have respective measurement leads (6, 7, 10) which are passed through the housing 4 and connected to an evaluation device 8 for processing the measurement signals.
It is understood that the foregoing description is that of the preferred embodiments of the invention and that various changes and modifications may be made thereto without departing from the spirit and scope of the invention as defined in the appended claims.
Claims (23)
1. An electrochemical measuring cell for determining ammonia or hydrazine in a fluid measuring sample present in the abient, the measuring cell comprising:
a housing having an opening directed toward the sample to be measured and defining an electrolyte chamber;
a soluble electrolyte contained in said chamber;
a membrane mounted on said housing for closing off said chamber to the ambient and being permeable to ammonia and hydrazine;
a measuring electrode and a counter electrode disposed in said chamber so as to be in spaced relationship to each other;
said soluble electrolyte being an aqueous solution of a hygroscopic salt of an alkali metal; and,
said measuring electrode having a cobalt oxide coating; and, said coating being formed on said measuring electrode so as to be in direct contact with said electrolyte.
2. The electrochemical measuring cell of claim 1, further comprising a reference electrode disposed in said electrolyte and having a coating containing cobalt oxide formed thereon.
3. The electrochemical measuring cell of claim 1, further comprising a reference electrode disposed in said electrolyte; and, at least one of said measuring electrode and said reference electrode each including a carrier made of a noble metal and said coating being electrolytically deposited on said carrier.
4. The electrochemical measuring cell of claim 1, further comprising a reference electrode disposed in said electrolyte; and, at least one of said measuring electrode and said reference electrode including a carrier containing a cobalt alloy and said coating being an oxide layer formed by oxidizing said alloy.
5. An electrochemical measuring cell for determining ammonia or hydrazine in a fluid measuring sample present in the ambient, the measuring cell comprising:
a housing having an opening directed toward the sample to be measured and defining an electrolyte chamber;
a soluble electrolyte contained in said chamber;
a membrane mounted on said housing for closing off said chamber to the ambient and being permeable to ammonia and hydrazine;
a measuring electrode and a counter electrode disposed in said chamber so as to be in spaced relationship to each other;
said soluble electrolyte being an aqueous solution of a hygroscopic salt of an alkali metal; and,
said electrolyte including a cobalt salt dissolved therein.
6. The electrochemical measuring cell of claim 5, said cobalt salt being cobalt nitrate.
7. An electrochemical measuring cell for determining ammonia or hydrazine in a fluid measuring sample present in the ambient, the measuring cell comprising:
a housing having an opening directed toward the sample to be measured and defining an electrolyte chamber;
a soluble electrolyte contained in said chamber;
a membrane mounted on said housing for closing off said chamber to the ambient and being permeable to ammonia and hydrazine;
a measuring electrode and a counter electrode disposed in said chamber so as to be in spaced relationship to each other;
said soluble electrolyte being an aqueous solution of a hygroscopic salt of an alkaline earth metal; and,
said hygroscopic salt having a concentration in said aqueous solution for obtaining a reduction of the freezing point of said solution down to a temperature of -50° C.
8. The electrochemical measuring cell of claim 7, wherein said hygroscopic salt has a cationic component and an anionic component; said cationic component being selected from the group consisting of magnesium and calcium; and, said anionic component being selected from the group consisting of a nitrate and chloride.
9. An electrochemical measuring cell for determining ammonia or hydrazine in a fluid measuring sample present in the ambient, the measuring cell comprising:
a housing having an opening directed toward the sample to be measured and defining an electrolyte chamber;
a soluble electrolyte contained in said chamber;
a membrane mounted on said housing for closing off said chamber to the ambient and being permeable to ammonia and hydrazine;
a measuring electrode and a counter electrode disposed in said chamber so as to be in spaced relationship to each other;
said soluble electrolyte being an aqueous solution of a hygroscopic salt of an alkaline earth metal; and,
said measuring electrode having a cobalt oxide coating; and, said coating being formed on said measuring electrode so as to be in direct contact with said electrolyte.
10. The electrochemical measuring cell of claim 9, further comprising a reference electrode disposed in said electrolyte and having a coating containing cobalt oxide formed thereon.
11. The electrochemical measuring cell of claim 9, further comprising a reference electrode disposed in said electrolyte; and, at least one of said measuring electrode and said reference electrode each including a carrier made of a noble metal and said coating being electrolytically deposited on said carrier.
12. The electrochemical measuring cell of claim 9, further comprising a reference electrode disposed in said electrolyte; and, at least one of said measuring electrode and said reference electrode including a carrier containing a cobalt alloy and said coating being an oxide layer formed by oxidizing said alloy.
13. An electrochemical measuring cell for determining ammonia or hydrazine in a fluid measuring sample present in the ambient, the measuring cell comprising:
a housing having an opening directed toward the sample to be measured and defining an electrolyte chamber;
a soluble electrolyte contained in said chamber;
a membrane mounted on said housing for closing off said chamber to the ambient and being permeable to ammonia and hydrazine;
a measuring electrode and a counter electrode disposed in said chamber so as to be in spaced relationship to each other;
said soluble electrolyte being an aqueous solution of a hygroscopic salt of an alkaline earth metal; and,
said electrolyte including a cobalt salt dissolved therein.
14. The electrochemical measuring cell of claim 13, said cobalt salt being cobalt nitrate.
15. An electrochemical measuring cell for determining ammonia or hydrazine in a fluid measuring sample present in the ambient, the measuring cell comprising:
a housing having an opening directed toward the sample to be measured and defining an electrolyte chamber;
a soluble electrolyte contained in said chamber;
a membrane mounted on said housing for closing off said chamber to the ambient and being permeable to ammonia and hydrazine;
a measuring electrode and a counter electrode disposed in said chamber so as to be in spaced relationship to each other; and,
said soluble electrolyte being an aqueous solution of a mixture of a hygroscopic salt of an alkali metal and a hygroscopic salt of an alkaline earth metal.
16. The electrochemical measuring cell of claim 15, wherein said salt of said alkali metal has a cationic component and an anionic component; said cationic component being lithium; said salt of said alkaline earth metal has a cationic component and a anionic component; said cationic component being selected from the group consisting of magnesium and calcium; and, said anionic component being selected from the group consisting of a nitrate and chloride.
17. The electrochemical measuring cell of claim 15, said measuring electrode having a cobalt oxide coating; and, said coating being formed on said measuring electrode so as to be in direct contact with said electrolyte.
18. The electrochemical measuring cell of claim 17, further comprising a reference electrode disposed in said electrolyte and having a coating containing cobalt oxide formed thereon.
19. The electrochemical measuring cell of claim 17, further comprising a reference electrode disposed in said electrolyte; and, at least one of said measuring electrode and said reference electrode each including a carrier made of a noble metal and said coating being electrolytically deposited on said carrier.
20. The electrochemical measuring cell of claim 17, further comprising a reference electrode disposed in said electrolyte; and, at least one of said measuring electrode and said reference electrode including a carrier containing a cobalt alloy and said coating being an oxide layer formed by oxidizing said alloy.
21. The electrochemical measuring cell of claim 15, said electrolyte including a cobalt salt dissolved therein.
22. The electrochemical measuring cell of claim 21, said cobalt salt being cobalt nitrate.
23. The electrochemical measuring cell of claim 15, said mixture having a concentration in said aqueous solution for obtaining a reduction of the freezing point of said solution down to a temperature of -50° C.
Priority Applications (5)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US07/804,722 US5228974A (en) | 1989-04-29 | 1991-12-11 | Electrochemical measuring cell for determining ammonia or hydrazine in a measuring sample |
| DE4206940A DE4206940C2 (en) | 1991-12-11 | 1992-03-05 | Electrochemical measuring cell for the determination of ammonia or hydrazine in a test sample |
| EP92118137A EP0546291A1 (en) | 1991-12-11 | 1992-10-23 | Electrochemical measuring cell for the determination of ammonia or hydrazine in a sample |
| DE4238337A DE4238337C2 (en) | 1991-12-11 | 1992-11-13 | Electrochemical measuring cell for the determination of ammonia or hydrazine in a test sample |
| US08/019,764 US5344546A (en) | 1989-04-29 | 1993-02-19 | Electrical measuring cell for determinging ammonia, amines, hydrazine amines, hydrazine and hydrazine derivatives |
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE3914284 | 1989-04-29 | ||
| DE3914284A DE3914284A1 (en) | 1989-04-29 | 1989-04-29 | ELECTROCHEMICAL MEASURING CELL FOR DETERMINING AMMONIA OR HYDRAZINE IN A MEASURING SAMPLE |
| US07/507,755 US5076904A (en) | 1989-04-29 | 1990-04-12 | Electrochemical measuring cell for determining ammonia or hydrazine in a measuring sample |
| US07/804,722 US5228974A (en) | 1989-04-29 | 1991-12-11 | Electrochemical measuring cell for determining ammonia or hydrazine in a measuring sample |
Related Parent Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| US07/507,755 Continuation-In-Part US5076904A (en) | 1989-04-29 | 1990-04-12 | Electrochemical measuring cell for determining ammonia or hydrazine in a measuring sample |
Related Child Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| US08/019,764 Continuation-In-Part US5344546A (en) | 1989-04-29 | 1993-02-19 | Electrical measuring cell for determinging ammonia, amines, hydrazine amines, hydrazine and hydrazine derivatives |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| US5228974A true US5228974A (en) | 1993-07-20 |
Family
ID=25189666
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| US07/804,722 Expired - Lifetime US5228974A (en) | 1989-04-29 | 1991-12-11 | Electrochemical measuring cell for determining ammonia or hydrazine in a measuring sample |
Country Status (2)
| Country | Link |
|---|---|
| US (1) | US5228974A (en) |
| DE (1) | DE4206940C2 (en) |
Cited By (10)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2292805A (en) * | 1994-08-26 | 1996-03-06 | Mil Ram Techn Inc | Electrochemical cell for detecting toxic gas |
| US5650054A (en) * | 1995-01-31 | 1997-07-22 | Atwood Industries, Inc. | Low cost room temperature electrochemical carbon monoxide and toxic gas sensor with humidity compensation based on protonic conductive membranes |
| US6098523A (en) * | 1997-07-10 | 2000-08-08 | Draeger Safety, Inc. | Testing apparatus for gas sensors |
| WO2002031485A1 (en) * | 2000-10-13 | 2002-04-18 | Advanced Technology Materials, Inc. | Acid gas measuring sensors and method of making same |
| US20080255641A1 (en) * | 2007-03-12 | 2008-10-16 | Lma Medical Innovations Limited | Device and method for temperature management of heating pad systems |
| US20090301876A1 (en) * | 2006-11-01 | 2009-12-10 | Mark Wagner | Sensor and methods of making the same |
| US20100283134A1 (en) * | 2009-05-06 | 2010-11-11 | Infineon Technologies North America Corp. | High Power Ceramic on Copper Package |
| US20110226619A1 (en) * | 2008-12-01 | 2011-09-22 | Msa Auer Gmbh | Electrochemical Gas Sensors with Ionic Liquid Electrolyte Systems |
| US8623189B2 (en) | 2008-12-01 | 2014-01-07 | Msa Auer Gmbh | Electrochemical gas sensor with an ionic liquid electrolyte system including at least one monoalkylammonium, dialkylammonium, or trialkylammonium cation |
| US9408939B2 (en) | 2013-03-15 | 2016-08-09 | Medline Industries, Inc. | Anti-microbial air processor for a personal patient warming apparatus |
Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3260656A (en) * | 1962-09-27 | 1966-07-12 | Corning Glass Works | Method and apparatus for electrolytically determining a species in a fluid |
| US3515658A (en) * | 1968-01-26 | 1970-06-02 | Honeywell Inc | Electrochemical sensor |
| US3830718A (en) * | 1973-03-22 | 1974-08-20 | Orion Research | Ammonia sensor |
| US4900405A (en) * | 1987-07-15 | 1990-02-13 | Sri International | Surface type microelectronic gas and vapor sensor |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3649505A (en) * | 1969-03-03 | 1972-03-14 | Beckman Instruments Inc | Ammonia sensor |
| DE3841622A1 (en) * | 1988-12-10 | 1990-06-13 | Draegerwerk Ag | ELECTROCHEMICAL MEASURING CELL FOR THE AMPEROMETRIC DETERMINATION OF AMMONIA AND ITS DERIVATIVES |
| DE3914284A1 (en) * | 1989-04-29 | 1990-10-31 | Draegerwerk Ag | ELECTROCHEMICAL MEASURING CELL FOR DETERMINING AMMONIA OR HYDRAZINE IN A MEASURING SAMPLE |
| DE3937635A1 (en) * | 1989-11-11 | 1991-05-16 | Fraunhofer Ges Forschung | Determination of gas esp. ammonia in air - using calibrated pH-selective glass membrane measuring electrode |
-
1991
- 1991-12-11 US US07/804,722 patent/US5228974A/en not_active Expired - Lifetime
-
1992
- 1992-03-05 DE DE4206940A patent/DE4206940C2/en not_active Expired - Fee Related
Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3260656A (en) * | 1962-09-27 | 1966-07-12 | Corning Glass Works | Method and apparatus for electrolytically determining a species in a fluid |
| US3515658A (en) * | 1968-01-26 | 1970-06-02 | Honeywell Inc | Electrochemical sensor |
| US3830718A (en) * | 1973-03-22 | 1974-08-20 | Orion Research | Ammonia sensor |
| US4900405A (en) * | 1987-07-15 | 1990-02-13 | Sri International | Surface type microelectronic gas and vapor sensor |
Cited By (18)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2292805B (en) * | 1994-08-26 | 1998-09-09 | Mil Ram Techn Inc | Method and apparatus for the detection of toxic gases |
| GB2292805A (en) * | 1994-08-26 | 1996-03-06 | Mil Ram Techn Inc | Electrochemical cell for detecting toxic gas |
| US5650054A (en) * | 1995-01-31 | 1997-07-22 | Atwood Industries, Inc. | Low cost room temperature electrochemical carbon monoxide and toxic gas sensor with humidity compensation based on protonic conductive membranes |
| USRE45186E1 (en) * | 1995-01-31 | 2014-10-14 | Atwood Mobile Products Inc. | Low cost room temperature electrochemical carbon monoxide and toxic gas sensor with humidity compensation based on protonic conductive membranes |
| US6098523A (en) * | 1997-07-10 | 2000-08-08 | Draeger Safety, Inc. | Testing apparatus for gas sensors |
| WO2002031485A1 (en) * | 2000-10-13 | 2002-04-18 | Advanced Technology Materials, Inc. | Acid gas measuring sensors and method of making same |
| US6423209B1 (en) * | 2000-10-13 | 2002-07-23 | Advanced Technology Materials, Inc. | Acid gas measuring sensors and method of using same |
| US8266795B2 (en) | 2006-11-01 | 2012-09-18 | Sensorcon, Inc. | Methods of making an electrochemical gas sensor |
| US20090301876A1 (en) * | 2006-11-01 | 2009-12-10 | Mark Wagner | Sensor and methods of making the same |
| US20130073012A1 (en) * | 2007-03-12 | 2013-03-21 | Medline Industries, Inc. | Device and Method for Temperature Management of Heating Pad Systems |
| US20080255641A1 (en) * | 2007-03-12 | 2008-10-16 | Lma Medical Innovations Limited | Device and method for temperature management of heating pad systems |
| US20110226619A1 (en) * | 2008-12-01 | 2011-09-22 | Msa Auer Gmbh | Electrochemical Gas Sensors with Ionic Liquid Electrolyte Systems |
| US8623189B2 (en) | 2008-12-01 | 2014-01-07 | Msa Auer Gmbh | Electrochemical gas sensor with an ionic liquid electrolyte system including at least one monoalkylammonium, dialkylammonium, or trialkylammonium cation |
| US9063079B2 (en) | 2008-12-01 | 2015-06-23 | Msa Europe Gmbh | Electrochemical gas sensors with ionic liquid electrolyte systems |
| US9945806B2 (en) | 2008-12-01 | 2018-04-17 | Msa Europe Gmbh | Electrochemical gas sensors with ionic liquid electrolyte systems |
| US8110445B2 (en) | 2009-05-06 | 2012-02-07 | Infineon Technologies Ag | High power ceramic on copper package |
| US20100283134A1 (en) * | 2009-05-06 | 2010-11-11 | Infineon Technologies North America Corp. | High Power Ceramic on Copper Package |
| US9408939B2 (en) | 2013-03-15 | 2016-08-09 | Medline Industries, Inc. | Anti-microbial air processor for a personal patient warming apparatus |
Also Published As
| Publication number | Publication date |
|---|---|
| DE4206940C2 (en) | 2001-02-01 |
| DE4206940A1 (en) | 1993-06-17 |
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